Poly(3-hexylthiophene)/single-walled carbon nanotube (P3HT/SWNT) materials are synthesized using an in-situ Grignard metathesis approach. The structural properties and photophysics of the materials are studied using a multitude of techniques, including H-1 NMR, FTIR, UV-vis absorption, Raman, photoluminescence (PL), and transient absorption spectroscopies. P3HT/SWNT composites with high P3HT regioregularity (rr>96%) are observed. Raman spectroscopic data on the solid samples reveals an increase in the dispersion rate parameter with increasing SWNT concentration, thereby indicating close overlap and strong interactions between P3HT and the carbon nanotubes. Changes in the solution-phase PL quantum yields and excited-state lifetimes relative to pure P3HT support these conclusions, and indicate that strong interactions persist even after the composites are dispersed in organic solvents. The high regioregularity and enhanced P3HT-SWNT interactions are promising attributes for improving the morphology and efficiency of functional P3HT/SWNT materials. (c) 2013 Wiley Periodicals, Inc. J. Polym. Sci. Part B: Polym. Phys. 2014, 52, 310-320